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Bicycle Parts: Chains, Gears & Ball Bearings : How Spokes Fail on a Bicycle

Bicycle Parts: Chains, Gears & Ball Bearings : How Spokes Fail on a Bicycle


Charles McMahon for Expert Village. We’re
talking about how bicycle are put together. If you want more information you can look
at the college level textbook on merionmedia.com. Well, here is what happens when you are on
a bicycle riding, of course the wheels going around. The spokes that point downward will
be unloaded a little bit, in other words it will get a less tension and the other spokes
will get a little bit more tension to make up with the unloading of the downwards spokes.
So what is happening, if you look at any one spoke, when the wheel turns, when it is down,
it is less tension, as it turns it is more tension, more tension, more tension, less
tension, more tension, more tension, more tension, less tension, so what this mean is
that the spoke is stretched a lot and then a little less, then lot, and little less every
time the wheel goes around, this is called cyclic loading. And you know if you ever took
a piece of wire, you bend it back and forth a lot and it breaks, of course you bending
it much more than these spokes are stretched and unstretched. But if you are a rider who
rides a whole lot, if you are a very serious bicyclist, from time to time you may break
a spoke and the spoke will either break normally up in the threaded region because the threads
are stress concentrators, this is called fatigue failure, or possibly down here, this is where
the stress is highest, either here or up in here. So the spoke breaks obviously you have
to take it out and replace the spoke and true up the wheel again, so one of the ways that
spokes can fail is by fatigue, cyclic loading and but it is only an issue for somebody who
does an awful lot of riding. The other way they could fail is by corrosion and we will
talk about that later in another segment.

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